Argulus in the Tay District, 2006

Transcription

1 Argulus in the Tay District, 2006 K. Birkeland and D. Summers (photo courtesy of Fisheries Research Services) Summary In August 2006 some specimens of the species Argulus coregoni were found on wild fish in the lower River Earn (Dupplin), the lower Tay (Islamouth) and the lower River Isla (Links Farm). This species was previously reported by Fisheries Research Services to occur in the lower Earn and lower Tay. Another species, Argulus foliaceus, was found in Fingask Loch, Blairgowrie. This species was found in the 1990s in Sandyknowes Fishery, Bridge of Earn, and has more recently been reported in Lindores Loch, Fife. Despite initial concerns, the Argulus in Fingask Loch will, therefore, not have come from those now endemic in the Isla system, since they are different species. Likewise, Fingask Loch will not be a source of infection of the River Isla or the Tay. The effects of the now endemic Argulus coregoni on river fish locally are unknown, but will be worse in long dry summers. Argulus foliaceus pose a significant threat to small stillwater fisheries. Rigorous controls are required to ensure that Argulus foliaceus does not spread further through either stocked fish, plants, anglers tackle etc.

2 Introduction This paper describes the results of a survey of the distribution of the freshwater louse, Argulus, within the Tay District during the summer of It was conducted by Tay District Salmon Fisheries Board staff under contract to the Tay Foundation. Biology Argulus, the freshwater louse, is a genus of freshwater lice found throughout the world. Contrary to its nick-name it is not a louse but a freshwater crustacean parasite found on a wide range of freshwater fish species. Adult Argulus lay their eggs on some surface like a stone or plant leaves. Their incubation is temperature dependent and they may hatch quickly in warm summer weather. After hatching the tiny Argulus are little bigger than a full stop on this page but they seek fish on whose skins they cling to and feed on. Their level of activity and growth is again dependent on temperature and, in Scotland, temperatures are only really high enough in summer. The young Argulus, especially, are poorly able to withstand currents, therefore they probably only survive in stillwaters, in marginal or backwater areas of rivers, slow flowing pools or among submerged vegetation. In Britain, Argulus seem to first appear in the late spring when young hatch out from eggs laid the previous autumn which have lain dormant over winter. However, with increasing temperature in early summer the first generation of Argulus may themselves reach breeding age within a few weeks and then give rise to a subsequent generation and so on. Argulus feed by puncturing the skin of fish and sucking out blood. Low levels of infestation might only result in discomfort but heavy infestation can ultimately result in the death of a fish. Argulus can cause severe infestation in places where host fish are abundant and easily found and high temperatures prevail for a long enough period to allow the summer population to mushroom. More detailed information on their biology can be found in Taylor, Sommerville and Wootten (2005). Distribution Of the 143 Argulus species described so far only three are found in the UK. Two of these, Argulus foliaceus and Argulus coregoni are regarded as native to the UK, though non-native to northern Scotland at least. The non-native Argulus japonicus most likely was introduced to Britain from the Far East through the ornamental fish trade. There is as yet no record of this latter species from Scotland (Taylor et al. 2005). A. coregoni have been present in the River Clyde since at least the beginning of the twentieth century (although they were initially misidentified as A. foliaceus) and A. foliaceus had been reported in several stillwaters in central and southern Scotland and also the Union and the Forth Clyde canals by the 1960s (Campbell 1971). In 1971 the Clyde was still the only place in Scotland known to have of A. Coregoni, although Campbell noted that perhaps they might been overlooked elsewhere. It is not known exactly how long Argulus have been present in the Tay District, but A. coregoni have apparently been present in the lower Earn for several decades (A. Walker pers. comm.). It is not known whether it may just have gone overlooked or introduced by some means. On occasions some significant infestation of fish may have occurred on the Earn. One angler we spoke to recalled seeing approximately 200 Argulus on a brown trout he caught in that river in By the mid 1990s Argulus were also known to be present in Glenfarg Reservoir, which is fed by water pumped up from the lower reaches of the River Earn (Northcott and Walker no date).

3 In the summer of 1994 stocked rainbow trout at Sandyknowes Fishery at Bridge of Earn started behaving oddly, swimming in circles near the surface of the loch. Some specimens removed from the loch were covered in Argulus, later identified as A. foliaceus. The fish suffered severe scale loss, fin damage and lesions due to the lice feeding activity, many were moribund. Large numbers of dead sticklebacks were also seen. The outbreak was associated with a prolonged period of dry and warm weather, when the temperature in the loch reached more than 20 o C. A similar outbreak on trout and sticklebacks also occurred at Sandyknowes in summer of 1995, leading to a temporary closure of the fishery (Northcott, Lyndon and Campbell 1997, Northcott and Walker no date). Initially it was thought that Argulus may have entered the fishery on roach which may have entered from the River Earn during large floods in 1993 (Northcott, Lyndon and Campbell 1997). In 1995 Fisheries Research Services then performed surveys at a number of locations on the Earn and found that Argulus seemed quite common on salmonids especially around Bridge of Earn but they seemed relatively scarce by Auchterader and FRS speculated they were probably not established in the upper Earn. However, all the Argulus in the Earn were of the coregoni species. FRS also found this to be the species present in Glenfarg Reservoir (Northcott and Walker 1996, Northcott and Walker no date). They also found A. Coregoni in the lower part of the mainstem of the Tay including the Perth Harbour area. However, no Argulus were found in an oxbow pond near Bridge of Earn which is regularly flooded by the Earn. They also found that, on considering all their sampling sites, Argulus infestation on roach was low compared to salmonids and they concluded roach was not a preferred species. They also seemed to avoid minnows but not sticklebacks. It became clear, therefore, that the Argulus in Sandyknowes Fishery had not been introduced from the Earn by roach. It was suggested that they might have been brought in with weed or on grass carp, both of which had been brought up from England to this fishery (Northcott and Walker no date). After the mid 90s FRS seemed to pay relatively little attention to Argulus within the Tay District but reports increased again in recent years with infestations on salmon parr being reported on the lower Tay in the warm dry summer of 2005, and problems being reported at Lindores Fishery in Fife and Fingask Loch, a stocked trout loch near Blairgowrie. The situation had become so bad that rainbow trout are no longer stocked into Lindores during the summer. Consequently against this background the Tay Foundation commissioned this survey in 2006 to better establish the Argulus distribution within the Tay District. Methods During July and August 2006 Tay District Salmon Fisheries Board (TDSFB) staff searched rivers within the Tay Salmon Fisheries District for the occurrence of Argulus on local freshwater fish species. Warm days were selected since Argulus are more active in warm weather. To catch the fish and examine them for parasites, fish were either caught by flyfishing with small trout flies or electric fishing. In total 478 fish were caught from various river locations, mainly salmon parr, but brown trout (all age classes), grayling, minnows and stone loaches were also caught. After a fish was caught it was quickly transferred to a small plastic bucket as otherwise the Argulus could detach themselves from the fish. On one occasion an Argulus was seen swimming in the bucket the instant the fish was brought into the bucket, though on other occasions they seemed to be attached quite tenaciously. Whilst in the bucket the fish were examined for the presence of Argulus and any observed were removed from the fish and preserved in alcohol so that they could later be sexed and identified to species.

4 The intention was to concentrate efforts on those areas where Argulus were thought likely to be present; the lower Earn, the lower Tay, the lower Isla and the Lunan Burn - a tributary of the River Isla into which Fingask Loch drains. There was a particular concern that perhaps Fingask Loch might act as a reservoir of Argulus, infecting the Isla or the Tay. Ghillies on the River Tay also reported the presence of Argulus on salmon caught on their beats and specimens of Argulus were obtained by anglers fishing for rainbow trout on Fingask Loch. Results Most of the fish caught were parasite free and only a few Argulus specimens were ever found on the few infested fish. A. coregoni were found on a brown trout in the lower Earn (Dupplin), on salmon parr in the Tay (Islamouth), on grayling in the lower Isla (Links Farm). See Table 1 for more details. It was notable however that those fish with parasites were generally caught in relatively slow flowing areas. Since it was much easier to catch small fish with the fly in faster rather than in dead water areas, the degree of infestation may appear less than it really was. It was also noted that on landing one grayling into a bucket of water the Argulus on it quickly detached themselves. It is possible, therefore, that anglers may not be aware of the true extent of them. Ghillies also reported some specimens of A. coregoni on adult salmon on Islamouth, Glendelvine, Dunkeld House and Kinnaird, though of course they need not have acquired the parasites at these places. There is also an historic record of a coloured grilse trapped by FRS at Clunie Dam on 13 th September 1983 with one Argulus was present between adipose and tail, although it is not known which species (D. Stewart, FRS, pers.comm). However, the Argulus obtained off rainbow trout from Fingask Loch proved to be the other species, A. foliaceus, and are known to have been present in this loch for several years. An electrofishing survey in the Lunan Burn, into which the loch flows, failed to yield any Argulus at all (Table 1). While Argulus have never reached catastrophic levels in Fingask Loch (it is thought the depth of the loch may give the fish a cool water refuge from them) they are considered a problem for the fishery. Argulus are not present at Butterstone Loch, further up the Lunan system and the fishery manager there insists on rigorous biosecurity measures to prevent anglers inadvertently introducing it. Discussion It seems clear, therefore, that A. coregoni is now endemic in the lower Tay, Earn and Isla. The latter two rivers are probably particularly suited to them being relatively slow flowing and pooly. The extent to which they are a threat to fish in the river is not known. As far as juvenile salmon are concerned, since these prefer to live in riffles where Argulus probably would not do well, there may not be too much cause for concern. However, though they do prefer riffles, some salmon parr can and do occupy slower flowing reaches, especially larger parr, and could be adversely affected. However, those species which have a greater affinity for pools than salmon, for example trout or grayling, are likely to be most at risk of infestation. Infestation of adult salmon or sea trout could also increase the risk of fungal infections, to which they can be prone in hot dry weather. In this survey the numbers of A. coregoni found on any fish was in fact low. But, as mentioned previously, there have been reports from anglers of more serious levels of infestation with one Earn angler observing perhaps 200 specimens on a brown trout in Such a level of infestation would surely have been damaging. In 1989 there was a particularly dry spring and summer, and conditions may have been extremely good for

5 Argulus. Thus, increasing summer warmth perhaps if associated with drier weather, could lead to more serious problems in future. Another unanswered question is how some adult salmon acquired Argulus. Some of the infested fish were described by ghillies as having been fresh run. One likely candidate area for infection may be the upper, freshwater part, of the Tay estuary. Current speeds are relatively low in this area in summer, and indeed static at high tide. Unfortunately this area was not successfully sampled. Angling was tried downstream from the Friarton Bridge, but nothing was caught. A further attempt was planned for the Tay Street / Shore Road area of Perth, but unfortunately the weather broke a few days before the planned visit and the river was high and coloured. So, while A. coregoni may perhaps pose more of a threat to river fish in future if summers continue to get warmer, of more immediate concern are the effects on stillwaters. The spread of A. coregoni through the Tay system as a result of warmer summers and transport by fish (for example, migrating adult salmon), may result in more stillwaters ultimately being infected by that species. However, according to the literature A coregoni is considered more of a river species while A foliaceus seems more of a stillwater species. The spread of A foliaceus is however a seriously worrying development for stillwater fisheries. As to how A foliaceus entered the various stillwaters is still unknown. However, the initial view that it was introduced to Sandyknowes by wild roach from the Earn seems untenable, given that A foliaceus has yet to be found on a wild river fish in Tayside, that this species is apparently not noted as a riverine species and that roach are a poor host anyway. Curiously it was also suggested by some members of the Blairgowrie Angling Association that Argulus may have been introduced to Fingask Loch by roach coming in from the Lunan Burn. The common factor between the fisheries where A. foliaceus is present is that they all are or have been regularly stocked with rainbow trout. A possible reason for the spread A. foliaceus must surely be as a result of introductions of stocked fish. Even if it were the case that they were brought in with plants or grass carp in some instances as opposed to the rainbow trout themselves, the introduction would still be a result of the way these fisheries are managed. Therefore, tighter controls on fish transfers between fish farms and waters would be useful to restrict the spread of this parasite. References Campbell, A.D. (1971) The occurrence of Argulus (Crustacea: Branchiura) in Scotland. Journal of Fish Biology, 3, Northcott, S.J., Lyndon, A.R. and Campbell, A.D. (1997) An outbreak of freshwater lice, Argulus foliaceus L., seriously affecting a Scottish Stillwater fishery. Fisheries Management and Ecology, 4, Northcott, S.J. and Walker, A.F. (1997) The best laid plans of lice and men. Atlantic Salmon Trust Progress Report, December 1997, Northcott, S.J. and Walker, A.F. (no date) The occurrence of freshwater lice, Argulus spp., in both wild and put-and-take fisheries in the River Earn catchment. Unpublished report, Fisheries Research Services, Pitlochry. Taylor, N.G.H., Sommerville, C. and Wootten, R. (2005) A review of Argulus spp. occurring in UK freshwaters. Science Report SC990019/SR1. Environment Agency, Bristol.

6 Acknowledgements We wish to thank the various fishery owners / tenants for allowing access to their beats, in particular Dupplin Estates, Mr D. Morison and Mr M. Underwood. We are also particularly grateful to the Blairgowrie and Rattray Angling Association for providing Argulus samples from Fingask Loch. We are also grateful to the Tay Foundation for funding this project.

7 Figure 1. Locations where Argulus were found or reported in 2006 (red) and locations where fish were sampled but no Argulus were found.

8 Table 1: Overview of Argulus infestation on freshwater fish species within the Tay Salmon Fisheries District Site Grid ref Date Species caught Method used No fish caught No fish with Argulus Argulus species Prevalence (%) Abundance Intensity Max no lice Tay, Upper Salmon Parr Fly 25 0 Redgorton Tay, Taymount Salmon Parr Fly Brown Trout Fly Tay, Islamouth Salmon Parr Fly 14 2 A. coregoni Tay overall 65 2 A. coregoni Lunan, Marlee Road Bridge Lunan, Coupar Angus Bridge Lunan, Blairgowrie Road Bridge Brown Trout, trout parr, salmon parr E-fish Salmon Parr E-fish Salmon Fry E-fish 39 0 Trout Parr E-fish 14 0 Trout Fry E-fish 4 0 Stone loach E-fish 16 0 Minnow E-fish Salmon Parr E-fish 23 0 Salmon Fry E-fish 25 0 Trout Parr E-fish 6 0 Trout Fry E-fish 5 0 Stone loach E-fish No fish E-fish 0 Lunan, Mainstem by Fingask caught Lunan NO Minnows E-fish Eels E-fish Stoneloach E-fish Lunan overall Isla, Links Farm NO Salmon Fry E-fish 20 0 Minnow E-fish 16 0 Stoneloach E-fish 72 0 Stickleback E-fish 0

9 Isla, Links farm Grayling (>12 Fly 5 2 A. coregoni cm) Salmon Parr Fly 6 Isla, island NO Salmon Parr Fly 22 upstream of Links Farm Salmon Fry Fly 2 Grayling (<12 Fly 16 cm) Isla, Coupar Salmon Parr Fly 22 Angus Grayling (<12 cm) Fly 1 Isla overall A. coregoni Earn, Dupplin NO Salmon parr Fly 29 Grayling (<12cm) Fly 2 Brown Trout Fly 2 1 A. coregoni Earn overall 33 1 A. coregoni Prevalence: The percentage of fish in the sample infected by salmon lice Abundance: The mean number of salmon lice per fish in the whole sample Intensity: The mean number of salmon lice per infected fish Maximum: The maximum number of salmon lice found on a single fish in the sample